frizzen--
Good to see you made the body look seperate. I was also thinking If you ever made the truck articulate, having the cab and bed acually seperate could produce a really cool effect. Mounting the body peices could take some ingenuity though (as well as making it articulate).
I think putting a bed in the body would look really cool if there is enough room to make it a 1/4" or so deep. Any less would be kinda pointless. Then again, a cap or camper shell would look pretty original as well. I saw a post on RCMod where someone made a RV shell for their zip, but a camper on an existing body I have seen not.
If it were my truck, I would probably put in the bed and finish it off with a "Rhyno Lining" look alike, then build a cap/camper for the truck seperate so it can be dropped in and removed whenever you want (more like a real truck). A ball tow hitch made out of a small bead or bearing and a thin strip of bent plastic or metal might look pretty cool too!
edit: just look at the pics again, and realized that to put on a tow hitch, you would also require a rear bumper. Depends on how far you want to take this project I guess. It's just an idea.